1. Field of the Invention
The present invention relates to a display device, and more particularly, to a printing apparatus for manufacturing a liquid crystal display device and a method for forming patterns using the same.
2. Discussion of the Related Art
Among ultra-thin flat panel display devices having a thickness of a few tens of centimeters, liquid crystal display devices have a low operating voltage, low power consumption and are portable. Thus, liquid crystal display devices are widely used in various fields, such as monitors in notebook computers, space shuttles, and aircraft.
A liquid crystal display device includes a lower substrate, an upper substrate, and a liquid crystal layer formed between both substrates. The lower substrate includes gate wires and data wires, which cross each other to define pixel regions, formed thereon. Thin film transistors (TFTs) serving as switching elements are formed at the crossings of the gate wires and the data wires. Further, pixel electrodes are formed on the lower substrate, and are connected to the TFTs.
A shading layer for preventing light leakage at the gate wires, the data wires, and the TFT regions is formed on the upper substrate, and a color filter layer is formed on the shading layer, and a common electrode is formed on the color filter layer.
Manufacturing a liquid crystal display device includes various processes that are repeatedly performed. In general, to pattern the components, a general photolithography process is used. In the photolithography process, a pattern material layer is formed on a substrate, and a photosensitive film is stacked on the pattern material layer. Then, a mask having a designated pattern is located on the photosensitive film, and the photosensitive film is patterned to a shape corresponding to the mask by exposure and development. Thereafter, the pattern material layer is etched using the patterned photosensitive film as a mask.
The above photolithography process uses the photosensitive film and the mask having a designated pattern, thus increasing the production costs of the liquid crystal display device. Further, the photolithography process includes the development and the etching. Thus the photolithography process is complicated and takes a long time.
Accordingly, to solve the above drawbacks of the photolithography process, an alternative method for forming a pattern has been developed. For example, a method for forming a pattern using a printing roll has been proposed.
FIGS. 1A to 1C are cross-sectional views illustrating a printing process for forming a set of patterns on a substrate according to the related art. As shown in FIG. 1A, a pattern material 20 is applied to a printing roll 10 using a printing nozzle 30.
As shown in FIG. 1B, the printing roll 10, to which the pattern material 20 is applied, is applied to a printing plate 40, in which a designated figure is engraved. Then, a part 20b of the pattern material 20 is transcribed on protrusions of the printing plate 40, and the other part 20a of the pattern material 20 remains on the printing roll 10.
As shown in FIG. 1C, the printing roll 10 having the remaining pattern material 20a then is rotated on a substrate 50, thereby transcribing the remaining pattern material 20a on the substrate 50.
As described above, a pattern formed using the printing roll 10 requires the printing plate 40. However, to pattern various components of a liquid crystal display device into various shapes, the method as shown in FIGS. 1A to 1C using one printing roll and one printing plate takes a long time. Thus, a four-color printing apparatus for forming red, green and blue color filter layers and a black matrix layer has been proposed.
FIGS. 2A to 2D are cross-sectional views illustrating a printing process for forming four sets of patterns according to the related art. As shown in FIG. 2A, pattern materials 20 are respectively applied to printing rolls 10a, 10b, 10c, and 10d using printing nozzles 30a, 30b, 30c, and 30d. 
As shown in FIG. 2B, the printing rolls 10a, 10b, 10c, and 10d, to which the pattern materials 20 are applied, move to respectively rotate on printing plates 40a, 40b, 40c, and 40d. The printing plates 40a, 40b, 40c and 40d are placed on a stage 60.
Although not shown in FIGS. 2A to 2D, designated figures corresponding to patterns to be formed are respectively engraved in the printing plates 40a, 40b, 40c, and 40d, as shown in FIG. 1B. Then, one part of the pattern material 20 applied to each of the printing rolls 10a, 10b, 10c, and 10d is transcribed on protrusions of the corresponding one of the printing plates 40a, 40b, 40c, and 40d, and the other part of the pattern material 20 applied to each of the printing rolls 10a, 10b, 10c, and 10d remains on the corresponding one of the printing rolls 10a, 10b, 10c, and 10d. 
Thereafter, as shown in FIG. 2D, the printing rolls 10a, 10b, 10c, and 10d are sequentially rotated on a substrate 50, thereby sequentially transcribing the remaining pattern materials 20a of the printing rolls 10a, 10b, 10c, and 10d on the substrate 50. Accordingly, a pattern is formed on the substrate 50 using the printing roll 10.
As described above, the four-color printing apparatus forms four patterns by a single process, thereby shortening an overall process time. However, since the pattern materials 20b respectively remain on the protrusions of the printing plates 40a, 40b, 40c, and 40d after one printing process is completed, the engraving on the printing plates 40a, 40b, 40c and 40d deteriorates for a next printing process